1. Field of the Invention
The present invention relates to a compressor and a driving method thereof. More particularly, to a compressor including a sensorless motor and a driving method of the compressor.
2. Description of the Related Art
A conventional brushless direct current (BLDC) motor, used in a compressor, is a motor driven through switching by an electronic circuit using transistors, particularly metal oxide silicon field effect transistors (MOSFETs), instead of a brush and a commutator, which are important parts of a direct current (DC) motor. This type of motor operates to distribute current, which is supplied from a DC power supply, to a three or four-phase winding of the motor. To this end, the position of a rotator is detected, and based on the detected position, a switching operation of the transistors is controlled to adjust the current supplied to the three-phase winding of the motor. Thus, the rotation and the speed of the motor are controlled.
In order to drive the BLDC motor without a sensor for sensing a rotation speed of the motor or a position of a rotator of the motor, the rotation speed of the motor or the position of the rotator must be indirectly detected from a phase current or a terminal voltage supplied to the BLDC motor. One conventional method to detect the position of the rotator includes the use of counter electromotive force-related information. However, since the counter electromotive force is proportional to a rotation speed of the rotator, it can not be used to detect the position of the rotator when the rotator stops or rotates at a low speed. Accordingly, when the BLDC motor is initially started, the rotator of the motor is aligned to a specified position by supplying current to a winding of the motor for a predetermined period of time. Then, the BLDC motor in a stop state is synchronically accelerated until the magnitude of the counter electromotive force reaches a sufficiently detectable value.
Although the rotator is forced to be aligned initially, when the current is applied to the winding of the motor without accurate information on the position of the rotator, overcurrent may be generated when the position of the rotator is not correct. Accordingly, a torque pulsation having a large width may be generated. Such overcurrent generation lowers the efficiency of the motor.
In addition, since the rotator is forced to be aligned without accurate information on the position of the rotator, when the motor is started in a condition where any pressure exists in the motor, a large amount of current must be supplied to the motor for a long time and a start failure rate increases.